The difference between involved minus uninvolved serum free light chains (dFLC) has been established as invaluable hematologic parameter in systemic light chain amyloidosis (AL). However, patients with initial dFLC below 50mg/L are currently deemed not evaluable for response to therapy. Therefore, we aimed to characterize this subgroup and to define novel hematologic response parameters. We retrospectively analyzed 783 AL patients newly diagnosed at our center between 2002 and 2016. Patients with dFLC<50 showed a smaller bone marrow plasmacytosis (7% vs. 10%, p<0.001), but no significant differences in all analyzed chromosomal aberrations. Cardiac involvement was less frequent (45 vs. 80%, p<0.001) and less severe (Mayo2004 stage III: 18% vs. 51%, p<0.001), while kidney involvement was more prevalent (83% vs. 53%, p<0.001) and proteinuria was higher (7.3g/l vs. 5.0g/l, p<0.001). In multivariate analyses, dFLC<50 appeared as independent prognostic factor with respect to overall survival (HR=0.50, p=0.003) and renal survival (HR=0.56, p=0.020). Patients with dFLC<50 showed a higher proportion of complete hematologic response (aCR) after first-line therapy (39% vs. 9%, p<0.001). Receiver-operating characteristics (ROC) analysis identified a "low-dFLC partial remission" (dFLC<10 for patients with dFLC between 20mg/L and 50mg/L), which predicted overall and renal survival already at 3 months after start of therapy. Importantly, a parallel Italian study (companion paper) validated this new hematologic remission parameter. The outcome of prospective clinical trials might be adversely influenced by exclusion of the favorable clinical subgroup with initial dFLC<50. We propose the appreciation of dFLC in hematologic response assessment for all patients with a baseline dFLC>20.
This research output has an Altmetric Attention Score of 16. This is our high-level measure of the quality and quantity of online attention that it has received. This Attention Score, as well as the ranking and number of research outputs shown below, was calculated when the research output was last mentioned on 20 November 2025.
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